An interface fluid valve mechanism for a rotary piston machine is subject to internal leakage between the metal-to-metal interface sealing surfaces at both ends of the rotary valve member. For successful operation, the seal clearance or tolerance factor between the metal interface sealing surfaces is required to be an extremely thin dimension and difficult to maintain on a production basis.
It is a case of matching very thin tolerances between the metal interface sealing surfaces and is aggravated by expansion due to heat of friction between the metal-to-metal matched surfaces. Should the seal clearance be matched too tightly, it may bring about a galling situation between the metal interface surfaces. The practice has been to lap these metal interface sealing surfaces to a fine tolerance, which is costly.
The ideal seal situation or tolerance factor is to allow a limited amount of leakage between the metal-to-metal matched sealing surfaces for needed lubrication to prevent heat expansion and galling, but to prevent all excessive leakage beyond that required for needed lubrication.
Besides reducing the volumetric efficiency of the rotary piston machine, excessive leakage may tend to impede the successful operation of the commutating porting of the rotary valve member. The timing sequence of the "make" and "break" of the registration of the commutative porting may become hampered if excessive leakage keeps right on leaking regardless of the registration.
The present invention, which comprises a commutating interface valve at one end of the rotary valve member and a flat blank interface seal at the other end, is disposed to allow a limited amount of leakage for needed lubrication. All excessive leakage is precluded. The flat blank interface seal comprises a master surface and a servant surface interfacing each other. The master surface comprises hard metal and is disposed to resist frictional wear. The servant surface comprises soft metal and is disposed to be less resistant to frictional wear than that of the hard metal. The soft metal surface and the hard metal surface are disposed, when assembled, to make a tight metal-to-metal fit against each other, allowing substantially no leakage. Upon relative rotation between the surfaces, the soft metal surface is disposed to wear in against the hard metal surface and may be referred to a servant wear-in surface.
The instant that needed lubrication begins to seep or flow between the hard and soft metal surfaces, as it will do upon relative rubbing action therebetween, the wear action then stops, with the result that the soft metal surface is disposed to wear in, but not wear out. The wear-in clearance space between the hard and soft metal surfaces incident to wear-in of the soft metal surface, at the time needed lubrication begins to flow between the rubbing surfaces, is a measure of the tolerance factor. From the standpoint of controlled leakage which provides for needed lubrication, the tolerance factor or wear-in seal clearance becomes ideal, in that it wears to what the situation calls for, and even accommodates for the viscosity or thickness of the hydraulic fluid used in the rotary piston machine. The wear-in effect is that the hard metal surface burnishes the soft metal surface and makes it smooth. The soft metal surface, before it is burnished, may comprise a turning machine cut finish.
The hard metal surface is urged by fluid pressure in a direction away from the soft metal surface, consequently the soft metal surface is protected from wearing out.
An object of my invention is to provide a wear-in seal clearance or tolerance factor which allows for needed lubrication but excludes excessive leakage.
Another object is to provide a seal clearance which is disposed to wear in but not wear out.
Another object is to urge the hard metal surface in a direction away from the soft metal surface to protect the soft metal surface from wearing out.
Another object is to burnish the soft metal surface and make it smooth.
Another object is wherein the soft metal surface, prior to becoming burnished, comprises a turning machine cut finish.